The use of solid-phase sorbents, e.g., bonded silica, to extract an isolate, usually a chemical compound dissolved or otherwise dispersed in a liquid sample, is known. For example, U.S. Pat. No. 4,710,289--Wermuth et al. discloses a pre-column that has a sorbent packed by a frit. Similar systems are disclosed in Sorbent Extraction Technology, Analytichem International Inc., Harbor City, Calif. 90710 (1985) and Baker-10 SPE Applications Guide Vol. 1, J.T. Baker Chemical Co., Phillipsburg, NJ 08865 (1985). It is also known to use disposable columns, similar to the barrels of disposable medical syringes, that retain sorbent between discs of porous material or frits. These columns use a luer-type seal on the bottom, as described in ANSI/HIMA MD70.1 (1983).
However, these prior art systems have certain limitations and disadvantages. Prepared, disposable columns filled with particulate sorbent between frit layers exhibit a tendency wherein the top frit becomes displaced and voids form in the sorbent which, even when extremely small, can distort the results of an extraction and/or solution of the isolate. This problem is recognized by U.S. Pat. No. 4,655,917--Shackelford et al. Moreover, the prior art columns described above do not lend themselves for use in automated systems. The forces needed to disengage the luer taper seal have high variances due to the dimensional tolerances permitted under the above-referenced ANSI standard, and may require rotation about the axis of the luer taper to insure an adequate seal. These requirements do not facilitate handling using conventional robotic "grippers" or other types of automated apparatus. Additionally, modifications to the barrel shape of the syringe columns to allow for robotic manipulation have resulted in significant increase in column volume, thus resulting in reduced storage density within a rack or manipulating device.
Therefore, it would be desirable to create a device that would retain a sorbent bed without permitting voids to be created and that could be readily handled by automated systems. It is thus an object of the present invention to provide a solid phase extraction apparatus that is reliable and easy to use in both automated and manual systems, while providing a high degree of seal integrity and application flexibility. It is also an object of this invention to provide the ability for gas and liquid chromatograph autosamplers to manipulate a solid-phase extraction cartridge in a similar or improved manner to that used to manipulate standard sample vials. Another object of the present invention to provide a cartridge that can be manipulated in a storage density similar to that of standard sample vials. It is a further object of this invention to provide a cartridge that has a seal that requires sealing forces less than or equal to the magnitude required for luer seals, thereby permitting the present invention to be used in automated processes and to provide compatibility with existing semiautomatic and manual processes and apparatus. It is a still further object of this invention to provide means within a cartridge to prevent or severely limit the displacement of a frit disposed on top of the sorbent. Another object of this invention to provide a cartridge that permits a varying internal volume while maintaining a substantially constant external cartridge geometry, so that no handling modifications are necessary to accommodate different sorbent volumes.